～～～數學題～～～

1)第ｎ項=17-3(n-1)=20-3n
2)let 公差=f
b+e=26 -------2a+5f=26
a+c+d=29---------3a+5f=29
a=3
f=4

1) first term = 17, common difference = -3
T (n) = 17 - 3(n-1) = 21 - 3n

2) 設公差為y,
b+e = 26
(a+y) + (a+4y) = 26
2a+5y = 26 ..........(i)
a+c+d = 29, i.e. a+(a+2y)+(a+3y) = 29
3a+5y = 29 ..........(ii)
By solving (i), (ii), we have y = 4

１）求等差數列１７，１４，１１，．．．的第ｎ項
n=17+(n-1)(3)

２）a,b,c,d,e組成一等差數列。若b+e=26 及a+c+d=29, 求公差。
公差=29-26
=3

n=17+(n-1)(3)

公差=29-26
=3